Dialkyl dithiocarbamates as collectors in froth flotation



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US. Cl. 209-166 9 Claims ABSTRACT OF THE DISCLOSURE An ore flotation process employing a collector represented by Formula I:

a S R1l I-( SR2 (I) wherein R and R can be lower-alkyl, allyl or methallyl and at least one of R or R is lower-alkyl, and R can be hydrogen or lower-alkyl.

This invention relates to a method for concentrating minerals from ores by flotation. More particularly, the present invention relates to an ore flotation process employing as a collector or promoter a dithiocarbamate.

Flotation is a commonly employed process for concentrating minerals from ores. In a flotation process, the ore is crushed and ground to obtain a pulp. A collecting agent and a frothing agent which assist in separating minerals from the undesired or gangue portions of the ore in subsequent flotation steps are added to the ore. The pulp is then aerated to produce a froth at the surface thereof and the collector promotes the separation of the mineral values from the ore by causing the mineral values to adhere to the bubbles formed during this aeration step. The adherence of the mineral values is selectively accomplished so that the portion of the ore, not containing mineral values, does not adhere to the bubbles. The mineral-containing froth is collected and further processed to obtain the desired metals. That portion of the ore which is not carried over with the froth, usually identified as flotation tailings, is usually not further processed for extraction of metal values therefrom.

In flotation processes, it is desirable to recover as much mineral as possible from the ore while effecting the recovery in a selective manner. That is, it is desirable to recover as much of the mineral from the ore without carrying over undesirable portions of the ore. Presently known oily or water-insoluble collectors are allyl alkyl xanthates, alkyl esters of alkylthionocarbamates and (alkoxycarbonyl) alkyl xanthates. While a relatively large number of compounds within each of these classes are available as collectors, exhaustive studies have shown the most eflective oily collectors to be allyl amyl xanthate', o-isopropyl N-ethylthiocarbamate and (ethoxycarbonyl) ethyl xanthate. Although mineral recovery improvement from these collectors can be as low as only about one percent over other collectors, this small improvement is of great importance economically since commercial operations often handle as much as about 50,000 tons of ore daily. With the high throughput rates normally encountered in commercial flotation processes, relatively small improvements in the rate of mineral recovery result in the recovery of additional tons of minerals daily.

Obviously then, any collector which promotes improved mineral recovery, even though small, is very desirable and can be very advantageous in commercial flotation operations.

It is an object of the present invention to provide collecting agents which improve the selective recovery of States Patent Patented Sept. 2, 1969 mineral values from ores. It is a further object of the present invention to provide collecting agents which can be satisfactorily employed in present flotation processes. Further objects of the present invention will become evident in view of the following detailed discussion.

In accordance with the present invention, an ore flotation process is provided which utilizes a dithiocarbamate collecting agent, represented by Formula I:

wherein the R and R substituents can be lower-alkyl, allyl or methallyl and at least one of R or R is loweralkyl, and R can be hydrogen or lower-alkyl. The collector and a frother are added to the ore and intimately mixed therewith prior to and/or during the flotation step. The ore pulp-collector-frother mixture is then treated under conditions to form a froth. The froth selectively removes the mineral values from the ore and the mineral-rich froth is separated from the ore flotation pulp and recovered. The value-depleted pulp which remains in the flotation cell is removed. The mineral-rich froth is then further treated to recover the desired metal values. By the process of this invention, it has been found that both the amount of metal value which is recovered and the concentration of the mineral value in the froth are substantially increased over the processes which employ presently known collectors. Accordingly, the present invention provides substantial advantages over present processes.

The dithiocarbamate collectors of this invention can be employed in any base metal flotation process wherein a water-insoluble or oily collector is required. Exemplary ores which are processed by froth flotation with a waterinsoluble collector are sulfides and oxides of copper, zinc, molybdenum, lead, iron, nickel, cobalt and the like. Such ores may contain precious metal values. The dithiocarbamate collectors are employed in amounts of from about 0.002 lb./ton ore to about 0.25 lb./ton ore; preferably from about 0.01 lb./ ton ore to about 0.1 lb./ ton ore. The use of more than about 0.1 lb./ton ore dithiocarbamate collector generally does not improve recovery sufliciently to economically justify the additional collector cost while the use of less than about 0.002 lb./ton ore dithiocarbamate collector does not materially improve mineral separation.

In flotation processes, the particular collector employed generally varies with the type and metal content of the ore being processed. Some collectors find more universal use than others in that relatively high recoveries of mineral values are obtained for a large number of ores when these collectors are used and, thus, they are preferred. Of the dithiocarbamate collectors of this invention, S-allyl N- ethyldithiocarbamate, S-allyl N-isopropyldithiocarbamate and S-allyl N-methyldithiocarbamate promote greatly improved mineral value separation for a wide variety of ores and are thus preferred.

The dithiocarbamate collectors of this invention can be employed either alone or in conjunction with a watersoluble collector or other additive such as frothers. It is preferred to employ the dithiocarbamate collector with a water-soluble collect-or since the recovery of mineral values is improved over processes which employ either collector alone. Among the water-soluble collectors which can be employed are alkali metal xanthates such as sodium or potassium ethyl, isopropyl, secondary or isobutyl, amyl, or isoamyl, and hexyl xanthates and dithioprosphates such a dicresyl, diethyl, diisopropyl, disecondary or diisobutyl, diatmyl, or diisomayl, and dihexyl dithiophosphates as free acids or as sodium, potassium or ammonium salts, and also mercaptobenzothiazole derivatives.

- The water-soluble collector is employed with the waterinsoluble dithiocarbamate in amounts of between about 0.002 and about 0.25 lb./ ton ore; preferably between about 0.005 and about 0.1 lb/ ton ore based upon the weight of the ore in order to provide economic operation while promoting the improved mineral recovery.

The dithiocarbamate collectors may be used in combination with hydrocarbon oils and with other oily collectors such as allylxanthates, dialkylthionocarbamates and (alkoxycarbonyl)allylxanthates. Furthermore, the dithiocarbamate collectors of this invention can be added to the ore flotation process either alone or mixed with an emulsifier such as nonyl phenol-ethylene oxide condensates, organic sulfosuccinates or sulfosuccinamates.

In present froth flotation processes, a condition agent such as an alkali or an acid and a frothing agent are usually employed with the collecting agent. The conditioning agent adjusts the pH of the ore pulps so that better selectivity and/or increased recovery of values is obtained.

The frother is employed to produce a stable froth during the flotation steps. Suitable frothers which can be employed in this process are methyl isobutyl carbinol, polypropylene glycols and glycol ethers, pine oil and cresylic acid.

The dithiocarbamates of the present invention are obtained by first reacting carbon disulfide with an alkyl, allyl or methallyl amine in the presence of an alkali. The reaction is carried out in an aqueous medium at a temperature generally between about 25 C. and about 90 C., preferably between about 75 C. and about 85 C. Upon completion of the relation, the reaction mixture is cooled to below about 30 C., and an alkyl, allyl or methallyl halide is added thereto while maintaining the temperature of the reaction mixture below about 35 C. The hydrocarbon moiety of the halide attaches to the sulfur atom to form the desired dithiocarbamate. After all the allyl halide has been added, the reaction mixture is heated to about 60 C. to complete the reaction to dithiocarbamate product. The reaction mixture is then cooled to form an oily layer which may then be washed with Water and subsequently heated under vacuum to strip off any unreacted chloride. The product is covered usually as a light yellow oil.

The following examples are intended to illustrate the process of the present invention and are not intended to limit the same.

EXAMPLE 1 A Canadian copper ore, assaying about 1.4% copper, was ground to minus 65 mesh at about 60% solids. The pH was adjusted to 8.9 by the addition of lime. Following the addition of 0.022 lb./ton of methyl-isobutyl carbinol, 0.008 lb./ ton of a water-soluble dialkyl dithiophosphate collector and 0.016 lb./ton of one of the oily collectors set forth in Table I, the ore pulp was conditioned at 20% solids for 1 minute in a flotation cell. The following results were obtained after flotation for 4 minutes. A comparison of the dithiocarbamate with a thionocarbamate (the standard promotor for this ore) follows:

With the dithiocarbamate collector, both the recovery of copper and assay of the froth product were improved over the results obtained with the standard collector.

EXAMPLE 2 A Canadian copper ore assaying about 1.0 percent copper was ground to minus 65 mesh. The pH of the ore pulp was adjusted to 10.0 by lime addition. After addition of 0.03 lb./ton of collector, set forth in Table II,

4 the ore pulp conditioned for 2 minutes in a flotation machine. Then 0.06 lb./ton of methyl isobutyl-carbinol froth was added and the pulp again conditioned for 1 minute. The following results were obtained with the in dicated collectors after a 5 minute flotation period.

TABLE II Concentrate (percent Cu) Tailing,

percent Cu Collector 0.180 S-allyl N-et-hyldithiocarb at am e. 0. 158 S-allyl N-cyolohexyldithiocarbamatc. 0. 203 O-isopropyl N-ethyltllionocarbamate (standard).

Assay Recovery With the dithiocarbamate collectors, the recovery of copper was improved over the result obtained with the standard collector.

EXAMPLE 3 Separate samples of a copper ore from Western United States, assaying 0.80% copper, were ground to minus 65 mesh. The pH was adjusted to about 11 with lime. In each test, a particular collector was added in the amount of 0. 02 lb./ton together with 0.05 lb./ ton of polypropylene glycol frother. After flotation for 4 minutes and the removal of one concentrate, 0.008 lb./ ton of sodium isopropyl xanthate was aded. This was followed by a short conditioning period and another 4 minute float. The results are set forth in Table III.

results over the standard collector.

EXAMPLE 4 A copper ore from Utah, containing 0.76-0.79% Cu with chalcopyrite as the chief copper mineral, was ground to about minus 65 mesh, conditioned with 1.5 lb./ton lime, 0.03 lb./ton sodium cyanide, and 0.01-0.03 lb./ton promoter, 0.18 lb./ton cresylic acid as frother, and floated for 6 minutes in a laboratory Fagergren flotation machine to remove a copper concentrate. The pH of the flotation pulp was 10.8. The copper concentrate was dried and assayed for copper. The above method was followed in a series of tests comparing S-allyl N-ethyldithiocarbamate with isopropyl ethylthionocarbamate as copper promoters. The results of these tests, summarized in the Table IV, demonstrate that the dithiocarbamate gave higher copper recovery than the standard thionocarbamate promoter.

lb./ ton lime, 0.008 lb./ ton sodium isopropyl xanthate, and 0.02 lb./ ton of a collector set forth in Table V, 0.05 lb./ ton of a polyglycol frother and floated for 6 minutes in a laboratory Fagergren flotation machine to remove a copper concentrate.

The results of these flotation tests are given in Table V and show that the highest and most selective copper recovery was obtained with the dithiocarbamate promoter.

TABLE V Concentrate, percent Cu Tailing Collector (O. 02 lb./ton) Assay Recov. assay S-allyl N-ethyldithiocarbamate. 12. 13 94. 12 0. 050

(Ethoxy carbonyl) ethyl xanthate.- 11. 89 92. 29 0.069

Allyl amyl xanthate 9. 74 93. 47 0.056

EXAMPLE 6 A Canadian chalcopyrite ore, assaying 1.05-l.09% Cu and containing fractional percentages of molybdenum sulfide, was ground to minus 65 mesh at 60% solids in the presence of 0.67 lb./ton of lime and 0.02 lb./ton of sodium cyanide. After conditioning for 2 minutes with 0.03 lb./ton of a collector set forth in Table VI and then for 1 minute with 0.04 lb./ton of methyl isobutyl carbinol as frother, 0.02 lb./ton of potassium isopropyl Xanthate was added and the pulp was floated for 5 minutes in a Fagergren flotation machine. Then the pulp was con ditioned for 1 minute with an additional 0.02 lb./ton of potassium ethyl xanthate and 0.02 lb./ ton of the carbinol frother followed by a second 5 minute float.

Both thiocarbamate collectors gave improved results over the standard collector.

EXAMPLE 7 In a series of tests on a Canadian chalcopyrite ore assaying about 1.1% Cu, the effect of both the waterinsoluble collector alone and the combination of waterinsoluble collector with a water-soluble collector was demonstrated. In these tests, the ore was ground to minus 65 mesh for 7 minutes with 0.067 lb./ton of lime and 0.02 lb./ ton of sodium cyanide. The ore pulp was then conditioned for 2 minutes with 0.02 lb./ton of a waterinsoluble collector and 0.06 lb./ton of methyl isobutyl carbinol as frother and then floated for 5 minutes in a Fagergren flotation machine. A second concentrate was also removed following an additional 1 minute conditioning with 0.04 lb./ ton of potassium isopropyl Xanthate and 0.03 lb./ ton of the carbinol frother. The second float was also for 5 minutes. In Table VII below the results obtained using various water-insoluble collectors alone and after the Xanthate addition are shown.

The dithiocarbamate collectors used alone in the first float and after Xanthate addition in the second float gave higher copper recoveries than the thionocarbamate collector.

EXAMPLE 8 An Arizona copper ore, assaying about 0.80% Cu was ground to minus 65 mesh in the presence of 2.5

lb./ton lime and conditioned with 0.020.03 lb./ton of a dithiocarbamate collector, 0.008 lb./ton sodium isopropyl Xanthate, and 0.05 lb./ton of a polypropylene glycol frother and floated for 6 minutes in Fagergren flotation machine. In a series of separate tests, various dithiocarbamate promoters were used. The results of these tests are given in the following table and demonstrate the general applicability of the dithiocarbamate collectors for recovering copper.

TABLE VIII Concentrate Tailing Dithiocarbamate used (Percent Cu) Percgjnt u Type Lb./ton Assay Recovery Assay S-allyl N-methyl 0. 015 9. 87 91. 54 0. 072 S-methallyl N-methyL 0. 02 8. 88 91. 37 0. 073 S-allyl N-ethyl 0. 02 12. 51 91. 31 0. 075 S-methallyl N-ethyl. 0. 02 11. 15 91. 40 0. 070 S-allyl N,N-dimethyl 0. 02 11. 26 92. 18 0. 069 S-allyl N-propyl 0. 02 12. 31 91. 08 0.076 S-allyl N-isopropyl 0. 02 11. 36 91. 46 0. 073 Do 0. 025 9. 91 91. 34 0. 073 0. 03 9. 76 92.01 0. 070 0. 025 10. 03 91. 29 0. 075 0. 03 9. 91. 37 0. 075 S-allyl N-cyclohexyl. 0. 025 9. 89 92. 01 0. 070 S-allyl N-llexyl 0. 03 11. 29 91. 43 0. 074 S-allyl N-allyl 0. 025 10. 28 91. 62 0. 06 S-methyl N-isopropyl--. O. 02 11.00 89.80 0. 088

EXAMPLE 9 A Tennessee zinc ore, assaying about 7.0% Zn, was ground to minus 65 mesh and was conditioned for 5 minutes with 0.9 lb./ton copper sulfate pentahydrate and then for 2 minutes with a dithiocarbamate collector and finally for one minute with 0.06 lb./-ton of a polyglycol frother. The ore pulp then was floated for 5 minutes to remove a zinc concentrate. The results of these tests are shown in the following table and demonstrate the applicability of the dithiocarbamates as zinc collectors.

A lead ore from the Tristate district of the United States, assaying about 1.7 weight percent lead, was ground and floated in the presence of 0.02 lb./ton ore sodium isopropylx'anthate and 0.03 lb./ton ore S-allyl N-ethyldithiocarbamate as promotor and with 0.12 lb./ton ore pine oil as frother in a Fagergren flotation machine for a period of 5 minutes. A concentrate assaying 49.2 weight percent lead was obtained representing a recovery of 88.3 weight percent total load.

EXAMPLE 11 A copper ore from Southwestern United States which assayed about 0.7% copper was ground to minus 65 mesh in the presence of 1.5 lb./ton lime, 0.03 lb./ton sodium cyanide, 0.08 lb./ton of cresylic acid as frother and an amount of collector as indicated in Table XI. The pulp was floated for 6 minutes in the laboratory flotation cell to remove the copper concentrate which assayed for copper. This method was used for a series of tests in which S-allyl N-ethyldithiocarbamate was compared with sodium ethyldithiocarbamate. This example shows the superiority of waterinsoluble dithiocarbamates of this invention over the watersolub le sodium salt of the dithiocarbamate which has been used in the past as a flotation collector.

TABLE XI Assay, Percent Cu Permgit u C olleetor used Lb ton Conc. Tailing recovery S-allyl N-ethyldit-hiocarbarnate 0. 01 14. 1 0. 107 85. 9 Sodium ethyldithiocarbamate l 0. 01 9. 7 0. 55 20. 2 Do 0. 03 8. 1 0. 52 23 5 I claim:

1. A method for collecting metal values from metal ores which comprises mixing ground metal ore with Water to form an ore pulp, aerating said pulp in the presence of an effective amount of a dithiocarbamate as the sole collecting agent, said dithioo'arbamate having the formula:

wherein R is lower alkyl, R is a member selected from the group consisting of allyl and me-thallyl and R is a member selected from the group consisting of hydrogen and lower-alkyl and recovering metal values from the resulting froth.

2. The process of claim 1 wherein a water-soluble collector is present in the pulp along with the dithiocarbamate.

3. The process of claim 1 wherein the dithiocarbamate is an S-allyl N-alkyldithiocarbamate.

4. The process of claim 2 wherein the dithiocarlw'amate is an S-allyl N-alky ldithiocarbamate.

5. The process of claim 1 wherein the dithiocarbamate is S-allyl N-ethyldithiocarbamate.

6. The process of claim 2 wherein the dithiodarbamate is S-allyl N-ethyldithioc-arbamate and the watersoluble collector is a dithiophosphate.

7. The process of claim 2 wherein the dithiocarbamate is S-allyl N-ethyldithiocarbamate and the Watersoluble collector is a xanthate.

8. The process of claim 1 wherein the metal ore is a copper ore. t

9. The process of claim 2 wherein the metal ore is a copper ore.

References Cited UNITED STATES PATENTS 2,127,375 8/1938 Bousquet 260-455 2,134,706 11/1938 Derby 209'166 2,691,635 10/1954 Harris 209-466 X 2,808,931 10/1957 Booth 209--166 2,905,586 9/1959 Harman 260455 X 3,298,520 1/1967 Bikales 209-166 HARRY B. THORNTON, Primary Examiner ROBERT HALPER, Assistant Examiner 

